Making and breaking of couplings between pipe sections in a drilling rig

ABSTRACT

For making of breaking a coupling between a pipe section ( 1 ) and a pipe string ( 2 ) projecting from a rotary drilling rig into a bore in the lithosphere, the pipe section ( 1 ) is rotated relative to the pipe string ( 2 ) by applying a torque up to a make-up or breaking torque. Exertion of said torque generates a reactive torque in an opposite sense of rotation. Rotation induced by a motor ( 17; 50 ) is transferred to the pipe string ( 2 ) so that said pipe string ( 2 ) is rotated as well. The reactive torque is transferred to the pipe string ( 2 ) along a path bypassing the motor ( 17; 50 ). Thus, the make-up or breaking torque can be exerted without requiring a substantial change of the torque exerted to rotate the pipe string ( 2 ) at a constant rotational velocity in order to avoid changes of the rotational velocity of the pipe string ( 2 ). A pipe coupling device and a pipe handler for carrying out this method are described as well.

TECHNICAL FIELD

The invention relates to the making and breaking of connections betweenpipe sections and a pipe string projecting from a drilling rig in a borehole in the lithosphere, for instance in the course of drilling orlining oil or gas wells.

BACKGROUND ART

Drilling for oil or gas and lining of the well typically involves theintroduction of a large number of pipe sections or stands such as drillpipe sections and casing pipe sections into the well. The sections areeach time connected to a string of sections projecting into the wellafter having been brought into line with the pipe string. Each sectionmay be formed by a single joint or by a plurality of joints which havebeen connected to each other before being connected to the string.

During drilling, the string is typically rotated while mud is being fedto the string for instance to drive a mud motor of a drill bit at theextreme end of the string. Mud can also be fed to facilitateintroduction of the string into the bore hole. It is also known torotate a casing string during insertion into a bore hole.

Couplings between successive pipe sections are typically made or undoneby screwing the pipe sections onto the string or unscrewing the pipesections from the string. To reduce the number of rotations requires tomake or break a connection, the mating threads of the couplings areusually of a generally conical shape. The spinning of each section to beconnected or removed is typically carried out after having stoppedrotation of the string. Tongs such as Wheatherford tongs or a so-calledIron Roughneck are used to spin each pipe section to be connected and toexert the final or initial torque required to make or, respectively,break the connection.

The efficiency and effectivity of such operations is substantiallyimpaired by the interruption of the drilling or lining process requiredto connect or disconnect the next section. This is of particularimportance, because the drilling of a bore hole typically involves aplurality of tripping operations (extracting and re-introducing thestring) for inspection and/or replacement of the drill bit. Eachtripping operation includes the disconnection and connection of about50-300 sections. More specifically, stopping the rotation of the stringhas various adverse effects; such as unwinding if the pipe string is adrill string. After rotation of a drill string has been restarted, ittypically takes 10-30 minutes before a reasonably stable operatingequilibrium is reached. Moreover, stopping rotation of a string in abore hole increases the risk of the string getting stuck in the borehole. As such, the period between stopping the string and restarting thestring adds to the time required to couple or remove a pipe section aswell.

It is known from U.S. Pat. No. 3,708,020 to Adamson to keep a smalldrill string for taking cores of geological formations or concreterotating while drill pipe connections are made or released. However, theexertion of torques to make or break the connections between successivelengths of drill pipe disturbs the operating equilibrium of the rotatingdrill string, which adversely affects the rate of progress and the toollife of the drill bit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a possibility toreduce the time required to add or remove pipe string sections and toallow the connection between successive sections of the pipe string tobe made while substantially reducing the extent to which the operatingequilibrium of a rotating string in a bore hole is disturbed.

According to the present invention, this object is achieved by providinga method for making or breaking a coupling between a pipe section and apipe string projecting from a rotary drilling rig into a bore hole inthe lithosphere, in which the pipe section is rotated relative to thepipe string by applying a torque up to a make-up or breaking torque,exertion of that torque generates a reactive torque in an opposite senseof rotation, wherein rotation imparted by a motor is transferred to thepipe string so that the pipe string is rotated as well, and wherein thereactive torque is transferred to the pipe string along a path bypassingthe motor.

Another embodiment of the invention for achieving this object is formedby a pipe coupling unit for at least coupling or uncoupling a pipesection and a pipe string axially projecting from a rotary drilling riginto a bore hole in the lithosphere. This pipe coupling unit is providedwith:

a pipe string engaging structure for engaging the pipe string;

a pipe section engaging structure for engaging the pipe section, thepipe section engaging structure being coaxial with and rotatablerelative to the pipe string engaging structure and in a position axiallydifferent from the position of the pipe string engaging structure;

a rotationally stationary support structure rotatably supporting thepipe string engaging structure;

a pipe string drive including a drive motor operatively coupled to thepipe string engaging structure and to the rotationally fixed supportstructure for driving rotation of the pipe string engaging structurerelative to the rotationally fixed support structure; and

a pipe section drive for driving rotation of the pipe section engagingstructure relative to the pipe string engaging structure with a torqueup to a required make-up or breaking torque, which pipe section drivebeing arranged for transferring a reactive torque in response to thetorque up to a required make-up or breaking torque to the pipe stringengaging structure along a transfer path bypassing the motor for drivingrotation of the pipe string engaging structure.

Thus, the make-up or breaking torque is or can be exerted in a mannerwhich substantially reduces the extent to which the operatingequilibrium of the string rotating in the bore hole is disturbed.

According to particular modes of carrying out the invention, the pipesection to be coupled to the pipe string is gradually accelerated tosubstantially a rotational velocity at which the pipe string is rotatingbefore the make-up or breaking torque is applied and/or before anengaging structure for applying the make-up torque to the pipe sectionare brought in engagement with the pipe section. Thus disturbances ofthe operating equilibrium of the rotating pipe section are furtherreduced.

Further objects, modes, embodiments and details of the invention appearfrom the dependent claims and the description in which reference is madeto the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a half of an example of a pipecoupling unit according to the invention;

FIGS. 2-7 are schematic side views representing successive stages of themethod according to the invention; and

FIG. 8 is an interrupted cross-sectional side view of another example ofa pipe coupling unit according to the invention.

MODES FOR CARRYING OUT THE INVENTION

In FIGS. 2-7 a presently most preferred example of a rotary drilling rigfor drilling into the lithosphere and more in particular for drillingand lining oil and gas wells is schematically depicted in successivestages of an operation of adding a pipe section 1—in this case a singlejoint pipe section—to a pipe string 2. Further pipe section 1′ and 1″are stored in a pipe section dispenser 3 aside the pipe string 2.

The drilling rig has a well head 4. Above the well head a lower drillingtable 5 is mounted on leg structures 6 and vertically movable betweenheights of about 11 and 17 m above terrain level by changing theeffective length of the leg structures 6. The leg structures 6 includehydraulic cylinders and guide means separate thereof, which cylindersand guide means are known constructional details and therefore not shownor described. Other known linear transmission systems for drivingmovement in the direction of the pipe string, such as cable hoists andscrew transmission systems, can be used as well. Above the lowerdrilling table 5 an upper drilling table 7 is mounted on leg structures8 similar to the leg structures 6 of the lower drilling table 5 andvertically movable as well in essentially the same manner betweenheights of about 23 and 30 m above terrain level. Of course, otherheight ranges within which the tables can be moved can be selected inaccordance with requirements regarding the lengths of the pipe sections1.

Instead of tables movable by leg structures (for instance with hydraulicor screw drives), it is also possible to achieve the lift function indifferent manners, for instance by using a cable hoist system with aguide for the drilling tables. However, the use of legs for lifting andlowering the drilling tables is particularly suitable for drilling in aslanting or even horizontal orientation.

The lower drilling table 5 carries a rotatable clamp 9 from which thepipe string 2 (typically having a mass of at least 300,000 to 500,000 kgwhen at maximum length) can be suspended releasably. The clamp 9 isconnected to a drive 10 for driving rotation of the pipe string 2 andcan transfer a driving torque of about 15,000-25,000 Nm. Coaxially withthe clamp 9, a passage through the clamp 9 and the lower drilling table5 is provided through which passage the pipe string 2 extends when therig is in operation. The design of the clamping section of the clamp 9can in principle be similar to that of conventional spiders forstationary mounting on a rig floor. The drive 10 for driving rotation ofthe clamp 9 is of a design equal to the portion of the drive assembly inFIG. 1 which serves for driving rotation of a pipe string claspingstructure 13 relative to the drill table 7.

The upper drilling table 7 carries a pipe coupling unit 11 of which apresently most preferred example is shown in more detail in FIG. 1. Thepipe coupling unit 11 has a pipe section clasping structure 12 forengaging the pipe section 1. Coaxial with the pipe section claspingstructure 12 and in a position axially different from the position ofthe pipe section clasping structure 12 there is provided a pipe stringclasping structure 13 for engaging the pipe string 2. The design of thepipe section clasping structure 12 can for instance be essentiallyidentical to that of the wrench of a conventional device for the make-upand break-out of pipe string connections and is therefore not shown ordescribed. The pipe string clasping structure 13 can for instance beessentially identical to that of a known spider or elevator with activepower-assisted clamping to ensure sufficient traction also if the pipestring is still short and therefore has a little weight. Preferably,both clasping structures are capable of transferring a make-up torque ofup to 50,000 to 120,000 Nm to the respective engaged pipe portions. Thepipe section clasping structure 12 should preferably be capable ofretaining pipe sections against axial loads of at least 2,500 to 3,000kg. The pipe string clasping structure 13 should be able to carry thewhole weight of a pipe string suspended in a bore hole, which can be upto about 500,000 kg when the pipe string is at its full length.

The pipe string clasping structure 13 is rotatably supported by arotationally stationary support structure 14, bearings 15, 16 beingprovided between the pipe string clasping structure 13 and thestationary support structure 14. The stationary support structure 14, inturn, is mounted to the upper drilling table 7.

For rotating the pipe string clasping structure 13, a pipe string driveincluding a drive motor 17 coupled to the pipe string clasping structure13 and to the rotationally fixed support structure 14 is provided. Thepipe string drive further includes a toothed ring 18 provided on thepipe string clasping structure 13 and a gear wheel 19 meshing therewithand fixed to the drive shaft 20 of the motor 17. The motor 17 is anelectromotor connected to power cables 21.

The pipe section clasping structure 12 is rotatably supported relativeto the pipe string clasping structure 13 by a flange 22 integrallyconnected to the pipe string clasping structure 13 and lift pawls 23projecting inwardly from the flange 22. To drive the rotation of thepipe section clasping structure 12 relative to the pipe string claspingstructure 13, a pipe section drive including an electromotor 24connected to power cables 25, a gear wheel 26 mounted to a drive shaft27 of the electromotor 24 and a circular toothed flange 28 is provided.The drive is mounted in a support housing 29 integrally formed with theflange 22 and accordingly rotatable in unison with the pipe sectionclasping structure 12.

For feeding power to the electrometer 24, the power cables are connectedto stationary power cables 30 via sliding contacts 31, 32 on the supporthousing 29 and on the stationary support structure 14, which contacts31, 32 co-operate along circular tracks.

To facilitate rotation and axial displacement of the pipe sectionclasping structure 12 relative to the support housing 29, even at hightorques, cylindrical sleeve bearings 33 are provided between the pipesection clasping structure 12 and the support housing 29. Becauserelative axial movements of the cylindrical bearing surfaces inaccordance with the pitch of the coupling members is required only whenrelative rotational movement occurs, substantially no additionalfriction has to be overcome to obtain the required axial movement.

The motor 24 is selected to generate a torque up to a required make-uptorque and, in the opposite sense of rotation, up to a required break-uptorque. It is observed that if, for instance, quarter turn connectionsare used, the rotatability of the pipe section clasping structure 12relative to the pipe string clasping structure 13 can be limited toslightly more than a quarter turn, if the sections can be rotationallyaligned with the pipe, and to slightly more than a half turn if the pipesections are engaged in random rotational positions. Accordingly, thetoothed flange 28 need not form a full circle about the pipe sectionclasping structure 12.

The motor 24 of the pipe section drive is fixed to the support housingso that a reactive torque in response to the make-up or break-up torqueis transferred directly to the pipe string clasping structure 13 whilebypassing the motor 17 for driving rotation of the pipe string claspingstructure 13. Thus, the torque exerted for rotating a proximal pipesection relative to the pipe string has no substantial influence on therotational velocity of the pipe string. Side effects caused byaccelerations and decelerations of the pipe section are relatively smalland can for a major part be compensated by a quite simple speed controlof the motor 17. A particular advantage is that the motor 17 is notloaded with the relatively large make-up torque, which increases itslife span and generally allows selecting a less powerful motor.

Since a second motor 24, separate from the first motor 17 for drivingrotation of the pipe string clasping structure, is included in the pipesection drive for rotating the pipe section 1 with a torque up to themake-up or breaking torque, particularly little influence of thecoupling operating onto the rotational velocity of the pipe string 2 isobtained.

As this second motor 24 is supported by a support structure 29 connectedto the pipe string clasping structure 13 for rotation in unisontherewith, a simple and effective construction is provided fortransferring the reactive torque to the pipe string 2.

In operation, adding a pipe section 1 to a pipe string 2 starts with thepicking up of a pipe section 1 from the dispenser 3. For this purposeand for transferring pipe sections 1 from the dispenser 3 to theproximal end of the pipe string 2 projecting into a bore hole in thelithosphere and vice versa, a pipe handler 34 is provided (FIG. 2). Thispipe handler 34 includes a pipe section engagement structure 35 forreleasably engaging pipe sections to be transferred. To guide and drivethe pipe section engagement structure 35 between a position adjacent thedispenser 3 and a position and orientation in line with the pipe string2, a lift unit 36 is provided which is guided by vertical guide rails 37and which has an arm 38 pivotable about the guide 37. The dispenser 3,the carriage 36 and the rails 37 are shown in FIG. 2 only, but are to beconsidered as included in FIGS. 3-7 as well.

The pipe section handler 34 further includes a drive, schematicallydepicted by square 40 connected to the pipe section engagement structure35 for driving rotation of that pipe section engagement structure 35.According to the present example, the drive 40 is of essentially thesame design as that of a conventional Iron Roughneck which can be movedlaterally towards a pipe section and engaged thereto and vice versa.However, the skilled person will appreciate that many otherpossibilities of driving rotation of the pipe section engagementstructure 35 of the pipe section handler 34 are possible.

The pipe section handler 34 further includes a stabilizing arm 41projecting under the pipe section engagement structure 35 and having agripper 42 adjacent its lower end. This arm serves to counteractpendular motion of a pipe section 1 retained in the pipe sectionengagement structure 35.

While the pipe section is being transferred from the dispenser 3 to theproximal (in this case upper) end of the pipe string 2, rotation andaxial displacement of the pipe string 2 is continued. Initially, justafter a previous pipe section has been connected, the pipe string isdriven by the rotating spider clamp 9 on the lower drill table 5. Theupper end of the pipe string 2 is guided by a topmost guide (not shown)and guided by the vertical guide 37 as well. This situation isschematically shown in FIG. 2. For further details regarding the topmostguide, reference is made to applicant's co-pending PCT applicationentitled “Mud Circulation for Lithosphere Drilling”, PCT/NL97/00726, WO99/34091, published Aug. 7, 1999, and having the same filing date as thepresent invention.

Just before the lower drill table 5 has reached its lowest position, thepipe string clasping structure 13 is brought into engagement with theproximal end of the pipe string 2 and takes over the function of drivingthe pipe string 2. Subsequently, the lower drill table 5 is returned toits upper take-over position. This situation is schematically shown inFIG. 3.

As is shown in FIG. 4, the drill tables 5, 7 are gradually lowered whilethe pipe section 1 is transferred to a position in line with the pipestring 2. Rotation of the pipe string is driven by the motor 17 of thepipe coupling unit, which advantageous, because the need of a top drivefor rotating the pipe string is obviated. Lowering of the lower drilltable 5 may also be postponed until just before the pipe string 2 isengaged by the clamp 9 on the lower drill table 5.

In FIG. 5, the pipe section 1 has reached a position in line with thepipe string 2 but still remote therefrom. In this situation, the pipesection clasping structure 12 is lifted to a position spaced from thepipe string clasping structure 13 by moving the pawls 23 radially inwardusing drive units 43 (FIG. 1). To allow horizontal drilling as well, thedrive units are of a double acting type, i.e. capable of controllingmovements of the pawls 23 against inward and outward loads.

From that position, the pipe section 1 is lowered until its lowercoupling end is introduced into the pipe section clasping structure 12(FIG. 6). To avoid damage to the coupling ends, the internal shape ofthe pipe section clasping structure 12 is preferably such that itprevents the pipe section from passing below a predetermined level inthe pipe section clasping structure 12. When the pipe section 1 hasreached its desired level, the pipe section clasping structure 12 isoperated to engage the pipe section 1 and the pipe section equipmentstructure 35 of the pipe handler is released from the pipe section 1.Subsequently, the pipe coupling unit rotates the pipe section 1 relativeto the pipe string 2 to make the connection between these parts.

Because the pipe section 1 to be coupled to the pipe string 2 has beenaccelerated to substantially the same rotational velocity as therotational velocity of the pipe string 2 before the pipe section to becoupled is engaged or at least the make-up or breaking torque isapplied, wear of the pipe section clasping structure 12 is substantiallyreduced. Since the velocity difference which the pipe section 1 to becoupled has to overcome is relatively small, disturbances of thecontinuous rotation of the string 2 due to inertia of the acceleratednew pipe section 1 are substantially reduced as well. Such smalldisturbances can be cancelled out using so-called soft-torque drivecontrols, which are known in practice.

Then, the pipe section drive motor 24 is activated to rotate the pipesection 1 relative to the pipe string 2 by applying a torque up to apreset make-up torque. Preferably, changes in rotational velocity of thepipe section to be connected are carried out smoothly, to facilitateavoiding disturbances of the equilibrium of the string rotating in thebore hole, for instance by anticipating forces exerted due toacceleration or deceleration and the rotational inertia of the pipesection to be connected or disconnected. Exertion of that torquegenerates a reactive torque in an opposite sense of rotation. Thereactive torque is transferred directly to the pipe string 1 so that themotor 17, which drives the pipe string 2 continuously during thedrilling or lining process, is bypassed and continuous rotation of thepipe string 2 is not substantially influenced by the exerted make-uptorque.

While the pipe section 1 to be connected is rotated relative to the pipestring, the pawls 23 having bevelled ends are gradually retracted at apace corresponding to the pitch of the mating coupling ends, so that thepipe section is gradually lowered at a pace corresponding to the pitchof the mating coupling ends as well and axial loading of the weight of apipe section onto the coupling before it has been completed is avoided.

After the connection has been made, the rotating spider clamp 9 isbrought into engagement with the pipe string 2 and takes over thefunction of driving and carrying the pipe string 2 from the pipecoupling unit 11. Subsequently, the pipe handler 34 is moved away fromthe pipe string 2 in a direction radial to the string 2. The upperdrilling table 7 carrying the pipe coupling unit 11 is moved upwardalong the added pipe section 1.

Thus, subsequently to the coupling of a pipe section 1 to a pipe string2, the pipe coupling unit by which the make-up torque has been appliedis axially moved towards a proximal end of the pipe string 2 lengthenedby the added pipe section 1 and subsequently engages that proximal endof that lengthened pipe string 2 and exerts the reactive torque on thelengthened pipe string 2 upon coupling of a next pipe section 1 to thelengthened pipe string 2.

This provides the advantage that the clasping structures 12, 13 of thepipe coupling unit 11 can remain located around the pipe string 2. Inturn, this obviates the need of a side gate allowing the string and theclasping structures 12, 13 to move laterally into and out of engagement,and allows clasping structures of the pipe coupling unit to be of aclosed ring structure fully encircling a passage for receiving a pipe tobe engaged. Thus, the construction of the clasping structures 12, 13 canbe kept relatively simple and the full circumference of the pipe stringcan be gripped providing sufficient traction for the transfer of largetorques at relatively low normal pressures. The surface pressurerequired to achieve a desired traction can further be reduced byproviding the clasping structures 12, 13 with large jaw surfaces.

As the pipe coupling unit 11 and the pipe handler 34 move upward, theuppermost pipe section of the pipe string is guided by the gripper 42and the pawls 23 of the pipe coupling unit 11. As the pipe coupling unitreaches the coupling end portion of the pipe section, which has aslightly larger diameter, the pawls 23 are resiliently pushed back.

It is observed that in the present example, the pipe string is orientedvertically, but that the pipe string can also be oriented in a slantingor even horizontal orientation.

In FIG. 8, an alternative example 45 of a pipe coupling unit is shown.The pipe coupling unit 45 according to this example has a pipe sectionclasping structure 46 for engaging the pipe section 1 which is axiallymovable relative to and guided by an upper portion of a pipe stringclasping structure 47 for engaging the pipe string 2. The axial movementcan be carried out in accordance with the rotation imparted by the motor54 and the pitch of the pipe couplings, so that relative rotation of thepipe section clasping structure 46 relative to the pipe string claspingstructure 47 is associated to substantially the same axial displacementrelative tot he pipe string 2 as the pipe section 1.

Each time a pipe section has been connected or disconnected, the pipesection clasping structure 46 is rotated and thereby screwed back to itsrespective starting position.

The pipe string clasping structure 47 is rotatably supported by arotationally stationary support structure 49.

For rotating the pipe string clasping structure 47, a pipe string driveincluding a drive motor 50 coupled to the pipe string clasping structure47 and to the rotationally fixed support structure 49 is provided. Thepipe string drive further includes a toothed ring 51 provided on thepipe string clasping structure 13 and a gear wheel 52 meshing therewithand fixed to a drive line 53 of the pipe string drive. In the driveline, a corner transmission 55 is included for bring rotation impartedby the motor 50 into line with the axis of rotation of the pipe string2.

To drive the rotation of the pipe section clasping structure 46 relativeto the pipe string clasping structure 47, a pipe section drive includesa second electromotor 54 and a transmission chain with a cornertransmission 55, a drive shaft 56, a distributing transmission 57,further drive shafts 58, 59, gear wheels 60,61 mounted to respectivelythe drive shafts 58, 59 and toothed rings 51, 62 meshing with,respectively, the gear wheels 60, 61.

The distribution transmission 57 is adapted for driving the drive shaft58 projecting in one direction in a sense of rotation which is oppositeto the sense of rotation in which the drive shaft 59 projecting in thediametrically opposite direction is driven, but does not substantiallyinfluence rotation of the drive shafts 58,59 in unison. To this end, thedistribution transmission 57 is provided in the form of a differentialgear with a reversing transmission for one of the drive shafts 58,59.

The torques applied to the two drive shafts are substantially identical,as are the diameters of the gear wheels 60, 61 and of the toothed rings51, 62. Thus, if the motor 54 is driven and exerts a torque on the pipesection clasping structure 46, a reactive torque of substantiallyidentical magnitude is exerted on the pipe string clasping structure 47.Accordingly, the reactive torque is passed to the pipe string withoutaffecting the motor 50 which drives the continuous rotation of the pipestring 2 and velocity surges of the pipe string 2 are, at least for amajor part, avoided.

The gear wheel 60 meshing with the toothed ring 62 of the pipe sectionclasping structure 46 is slidably mounted to the drive shaft 58 to allowit to follow axial displacement of the toothed ring as it is screwedinto or out of the pipe string clasping structure 47. To ensure that thegear wheel 60 follows the axial movement of the toothed ring 62accurately, guide discs 65, 66 are mounted to the gear wheels onopposite sides thereof and coaxial therewith. These guide discs projectradially beyond the gear wheel 60 and overlap side surfaces of a flangeon which the toothed ring 62 of the pipe section clasping structure 46is located.

For guiding a pipe stem as the pipe coupling unit 45 is moved upwardalong a newly connected pipe section, guide blocks 63 are provided abovethe pipe section clasping structure 46 and around a passage 64 for thepipe sections. These guide blocks 63 are resiliently urged against thepipe stems by springs 65 and align a newly connected pipe section 1 withthe pipe string 2 until its free end is engaged by the pipe stringclasping structure 47. Vice versa, when pipe sections 1 are to beremoved from a pipe string 2, the guide blocks 63 provide alignmentafter a pipe section has been released by the pipe string clasping unit47 and until it is engaged by the pipe section clasping structure of thepipe handler.

It will be readily apparent to the skilled person that, although theabove examples relate to the drilling and lining of oil and gas wells,accordingly adapted modes of carrying out the present invention can alsobe used in connection with other ground drilling operations.

What is claimed is:
 1. A method for making or breaking a couplingbetween a pipe section and a pipe string projecting from a rotarydrilling rig into a bore hole in a lithosphere, in which the pipesection is rotated relative to the pipe string by applying a torque upto a make-up or breaking torque, exertion of said torque generates areactive torque in an opposite sense of rotation, wherein rotationimparted by a motor is transferred to said pipe string so that said pipestring is rotated as well, and wherein said reactive torque istransferred to said pipe string along a path bypassing said motor.
 2. Amethod according to claim 1, wherein said pipe section to be coupled tosaid pipe string is accelerated to substantially a rotational velocityat which the pipe string is rotating before said make-up or breakingtorque is applied.
 3. A method according to claim 1, wherein said pipesection to be coupled to said pipe string is accelerated tosubstantially a rotational velocity at which the pipe string is rotatingand subsequently a pipe section engaging structure for applying saidtorque to said pipe section to brought into engagement with said pipesection.
 4. A method according to claim 1, further including: subsequentto the coupling of said pipe section to said pipe string, the step ofaxially moving a pipe coupling unit by which said make-up torque andsaid reactive torque have been applied towards a proximal end of thepipe string lengthened by said pipe section; and subsequently coupling anext pipe section to the pipe string including the steps of engagingsaid proximal end of said lengthened pipe string and exerting saidreactive torque on said lengthened pipe string by said pipe couplingunit.
 5. A pipe coupling unit for at least coupling or uncoupling a pipesection and a pipe string axially projecting from a rotary drilling riginto a bore hole in the lithosphere, comprising: a pipe string engagingstructure for engaging the pipe string; a pipe section engagingstructure for engaging the pipe section, said pipe section engagingstructure being coaxial with and rotatable relative to said pipe stringengaging structure and in a position axially different from the positionof said pipe string engaging structure; a rotationally stationarysupport structure rotatably supporting said pipe string engagingstructure; a pipe string drive including a drive motor operativelycoupled to said pipe string engaging structure and to said rotationallyfixed support structure for driving rotation of said pipe stringengaging structure relative to said rotationally fixed supportstructure; and a pipe section drive for driving rotation of said pipesection engaging structure relative to said pipe string engagingstructure with a torque up to a required make-up or breaking torque,said pipe section drive being arranged for transferring a reactivetorque in response to said torque up to a required make-up or breakingtorque to said pipe string engaging structure along a transfer pathbypassing said motor for driving rotation of said pipe string engagingstructure.
 6. A pipe coupling unit according to claim 5, wherein saidengaging structures each form a closed ring structure fully encircling apassage for receiving a pipe to be engaged.
 7. A pipe coupling unitaccord to claim 5, wherein said pipe section drive includes a secondmotor, separate from said first motor for driving rotation of said pipestring engaging structure, for rotating said pipe section with a torqueup to said make-up or breaking torque.
 8. A pipe coupling unit accord toclaim 7, wherein said second motor is supported by a rotatable supportstructure connected to said pipe string engaging structure for rotationin unison therewith.
 9. A pipe coupling unit according to claim 8,wherein said rotatable support structure and said rotationallystationary support structure are provided with sliding contactsco-operating along a circular task.
 10. A pipe coupling unit accordingto claim 5, further including a pipe handler for transferring pipesections from a dispenser to a proximal end of said pipe stringprojecting into said bore hole in the lithosphere and vice versa,including a pipe section engagement structure for releasably engagingpipe sections to be transferred, a guide and drive structure for movingsaid pipe section engagement structure between a position adjacent saiddispenser and a position and orientation in-line with said pipe stringand a drive connected to said pipe section engaging structure fordriving rotation of said pipe section engagement structure.
 11. A pipecoupling unit according to claim 10, wherein said guide and drivestructure is further adapted for moving said pipe section engagementstructure in a direction in which, in operative condition, said pipesections are oriented when held in-line with said pipe string.